This invention relates to the field of laser radiation generation in the bands II and III, namely 2 to 5 μm and 8 to 12 μm, respectively.
Other than gas lasers, there are no other lasers at the present time covering this region; in particular there are no diode-pumped solid-state lasers covering the region.
The prior art consists of using laser sources emitting close to the visible range (1.060 μm) and converting this wavelength to infrared using nonlinear effects.
Thus, U.S. patent application Ser. No. 2003/0012491 is known; and describes a device able to generate laser radiation in the infrared range, and which has means for generating an optical signal to be amplified, means for generating a pumping optical signal, means for coupling these two signals, and means for amplification and conversion to infrared consisting of an optical fiber with at least 25 mole % chalcogenide having elements such as sulfur, selenium, tellurium, or combinations thereof.
By the stimulated Raman effect, the optical radiation from the coupler is amplified and its frequency is displaced in the optical fiber.
However, as shown in particular in Example 2 of said patent application, the frequency variation in such a fiber is small, namely 1.91 μm and 6.2 μm respectively at the output for input wavelengths of 1.83 μm and 5.4 μm.
Hence, to produce in the entire infrared spectrum, namely 2 to 12 μm, it is preferable to have, at the input, a beam with a frequency close to the desired frequency. Hence it is necessary to use lasers such as CO2 or HFDF. The implementation of such lasers is technically complex in the context of optoelectronic counter-measures, particularly on board aircraft, and they are bulky (space occupied; gas recycling). Moreover, such a device has practically no frequency agility because, at most, a small number of discrete frequencies are available at the outputs, yet such a property is essential in the context of optoelectronic counter-measures.